The present invention relates to ink jet printers. It finds particular application in conjunction with an ink jet printhead having a channel plate with an integral filter, and will be described with particular reference thereto. It is to be appreciated, however, that the invention may find further application in conjunction with other ink jet technologies, such as piezo ink jet, as well as microfluid transport devices used in biological, chemical, and pharmaceutical applications.
In the area of microfluidics, fluid carrying components are small, often in the range of 500 microns down to 1 micron or smaller. Microfluid transport devices may be destroyed or debilitated by the inadvertent introduction of foreign particles into the fluid path, where the particles are large enough to block or seriously impede fluid flow in the device. This problem is magnified in systems where fluids are transported from the macroscopic world into microscopic componentry.
Conventional thermal ink jet printing systems use thermal energy pulses to produce vapor bubbles in an ink-filled chamber that expels droplets from channel orifices of the printing system""s printhead. Such printheads include one or more ink-filled channels communicating at one end with a relatively small ink supply chamber or reservoir and having an orifice at the opposite end, commonly referred to as the nozzle. A thermal energy generator, typically a resistor, is located within the channels near the nozzle at a predetermined distance upstream therefrom. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. A meniscus is formed at each nozzle under a slight negative pressure to prevent ink from weeping therefrom.
Often, these thermal ink jet printheads are formed by mating two silicon substrates. One substrate, which is commonly referred to as a heater plate, contains an array of heater elements and associated electronics. The second substrate, which is commonly referred to as a channel plate, is a fluid directing portion containing a plurality of nozzle-defining channels and an ink inlet for providing ink from a source to the channels. The channel plate is typically fabricated by orientation dependent etching methods.
One of the problems associated with thermal ink jet technology is the sensitivity of ink droplet directionality to particulates in the ink. Print quality is directly related to accurate placement of the ink droplets on a recording medium and droplet directionality determines the accuracy of the ink droplet placement. Accordingly, filtration of the ink to prevent such particles from blocking the channels or nozzles is critical for good print quality. The dimensions of ink inlets to the die modules or substrates are much larger than the ink channels. Therefore, it is desirable to provide a filtering mechanism for filtering the ink at some point along the ink flow path from the ink manifold or manifold source to the ink channels. Any such filtering technique should also minimize air entrapment in the ink flow path. In order to provide better print resolution, channel and nozzle sizes have decreased, which places an even greater premium on ink filtration to eliminate yet smaller particles to maintain a given level of print quality.
Various devices and methods for reducing particle contamination have been employed. U.S. Pat. No. 4,864,329 to Kneezel et al. discloses a thermal ink jet printhead having a flat filter placed over the inlet thereof by a fabrication process, which laminates a wafer size filter to the aligned and bonded wafers containing a plurality of printheads. The individual printheads are obtained by a sectioning operation, which cuts through the two or more bonded wafers and the filter. The filter may be a woven mesh screen or, preferably, a nickel electroformed screen with a predetermined pore size. Because the filter covers one entire side of the printhead, a relatively large contact area prevents delamination and enables convenient leak-free sealing. However, electroformed screen filters having a pore size that is small enough to filter out particles of interest leads to filters that are very thin and subject to breakage during handling or wash steps. In addition, the preferred nickel embodiment is not compatible with certain inks, resulting in filter corrosion.
U.S. Pat. No. 6,139,674 to Markham et al. discloses a polyimide filter, formed of a laser-ablatable material, which is aligned and bonded to the ink inlet side of the substrate. In addition, U.S. Pat. No. 5,734,399 to Weber et al. discloses a particle filter within the photo polymer layer, that is, the layer that forms the channels or ink flow paths, which sits on top of the heater wafer. This filter includes a plurality of small pillars separated by a distance smaller than the smallest channel or nozzle dimension. However, these types of integral filters are inconvenient and somewhat ineffective for drop ejectors due to the tightly packed array of jets contained therein. Any filter with the same height as the jets, but with smaller openings, is going to exhibit a rather high ink flow impedance, which has an adverse effect on print quality.
The present invention contemplates a new and improved ink jet printhead having a plastic channel plate with an integral filter, which overcomes the above-referenced problems and others.
In accordance with one aspect of the present invention, a device for selectively applying droplets of at least one fluid to a medium includes an actuation layer for propelling droplets of fluid along a fluid path and an intermediate layer disposed adjacent the actuation layer. The intermediate layer defines a plurality of substantially parallel fluid flow channels extending along a first direction. A channel plate, which is disposed adjacent the intermediate layer, includes an integral filter having a plurality of filter elements extending toward the intermediate layer along a second direction perpendicular to the first direction.
In accordance with a more limited aspect of the present invention, the channel plate defines an fluid reservoir disposed on one side of the integral filter and a cross-flow channel disposed on a second side of the integral filter. The cross-flow channel extends along a third direction perpendicular to the first and second directions.
In accordance with another aspect of the present invention, an ink jet printhead includes a heater substrate having a plurality of heating elements and an intermediate layer, which defines a plurality of ink flow channels in fluid communication with a plurality of ink droplet emitting nozzles. A channel plate, which defines an ink reservoir, includes an integral filter disposed between the ink reservoir and the ink flow channels.
In accordance with another aspect of the present invention, a method of fabricating a printhead for use in an ink jet printing device includes the steps of providing a heater substrate having a plurality of heating elements and forming an intermediate layer over the heater substrate, where the intermediate layer defines a plurality of ink flow paths. The method further includes forming a plastic channel plate having at least one ink reservoir, an integral filter including a plurality of filter teeth, and at least one cross-flow channel. The channel plate is adhesively or mechanically secured to the intermediate layer.